The invention relates to a luminaire with an array red, green and blue light emitting diodes (LEDs), and more particularly to a white light emitting luminaire with a control system for adjusting the individual components to maintain a desired color balance (chromaticity).
U.S. Pat. No. 5,301,090 discloses an LED luminaire having an array of LEDs including a plurality of LEDs in each of the colors red, green, and blue. The LEDs for each color are wired in parallel and provided with a separate power supply, and a diffusion screen is provided over the array. The chromaticity of the assembly is manually controlled by three knobs for the respective colors; automatic control is not mentioned.
LEDs are semiconductor based; for a given drive current, light output varies from chip to chip, and also varies over the life of each chip. Light output also varies inversely with temperature, but not uniformly for each color. Finally, in a block of LEDs of a given color, the light output will vary if one or more of the LEDs fails. Given all the factors which can affect the color balance of any array of LEDs, it would be desirable to automatically monitor and regulate the color balance, especially in a white-light emitting luminaire.
It is known to control current to an array of LEDs in a given color based on temperature, for example in a traffic light. This scheme would be cumbersome in a luminaire having LEDs in a plurality of colors, because the temperature (and therefore the light intensity) does not vary uniformly for the various colors.
It would be desirable to automatically control the chromaticity of a white light emitting luminaire, without regard to the factors which cause the light outputs of the individual colors to vary.
It would further be desirable to automatically control the chromaticity without resorting to a spectrally resolving light measuring system such as a photodiode and filter for each of the respective colors.